Deformation devices of the type mentioned in the introduction are used, for example, but by no means exclusively, in steering columns of motor vehicles and are intended, on the one hand, to absorb kinetic energy occurring during a collision of the vehicle. On the other hand, deformation devices of this type are to prevent parts of the steering line or the steering wheel from penetrating into the passenger compartment because of deformations occurring in a collision and from leading to injury to the driver.
Such a deformation device is known, for example, from DE 198 33 421 C2. This prior-art deformation device, which forms part of the steering line of a motor vehicle, comprises a steering column jacket and a conical component, wherein the conical component can penetrate into the steering column jacket in case of a collision of the vehicle while the end of the steering column jacket expands. In case of a correspondingly deep penetration of the conical component into the steering column jacket, the steering column jacket is able to be pulled apart along predetermined breaking points, which are formed by groove-like weakened areas of material, after which the steering column jacket is rolled up in strips because of the special shape of the conical component. Kinetic energy is dissipated in a defined manner due to the expanding, pulling apart and rolling up, and paths of deformation due to the collision are absorbed in the steering line in a defined manner, without parts of the steering line or the steering wheel penetrating into the passenger compartment.
The value of the breakaway force of the connection between the cone and the steering column jacket, which is designed as a press fit, is decisive for the proper function of such deformation devices. This breakaway force must not exceed, under any circumstances, certain maximum values, which depend, for example, on the manner of anchoring of the cone at the cockpit or physiological conditions of the human upper body, because there is otherwise a risk of severe injuries to the driver, for example, because of the penetration of the steering wheel into the passenger compartment or because of unacceptably strong forces of resistance of the steering wheel during the impact of the upper body or the head on the steering wheel. The maximum allowable breakaway force is thus one of the decisive factors for dimensioning the press fit between the cone and the steering column jacket.
However, the maximum torques that can be transmitted between the cone and the steering column jacket by frictional engagement is automatically also limited with the dimensioning of the press fit connection between the cone and the steering column jacket, which is thus inevitably limited as well. However, it may be desirable under certain circumstances in case of unchanged value of the breakaway force between the cone and the steering column jacket in the axial direction to make it possible to transmit higher torques between the steering column jacket and the cone. This happens, for example, when the steering column jacket is to be used for the torsional stabilization of other assembly units arranged at the cone or at the upper steering column.
Another case, in which the transmission of high torques between the steering column jacket and the cone is important, is the use of such a deformation device, for example, in a drag link, in which case the steering column jacket assumes both the deformation and energy absorption functions in a collision and the torque transmission function for steering movements during normal operation of the vehicle. Another aspect in relation to the transmission of increased torques is the increasing use of electric power steering, whose drive is often no longer arranged in the area of the steering gear but rather in the area of the upper steering column. As a result, it is necessary to continuously transmit not only the steering torque applied by the driver but also the entire steering torque via the largest part of the steering line, which likewise imposes increased requirements on the torsional strength of the connection between the cone and the steering column jacket.